Christianity in the Roman Empire

Christianity in the Roman Empire was an important religion which evolved from being a marginal, persecuted faith in the 1st century to becoming the state religion during the late 4th century. Christianity originated in the Roman province of Iudaea, where the Jewish rabbi Jesus spread the Gospel ("good news") to fellow Jews and preached about the arrival of the Messiah, God's plan to save humanity from its sins, and the steps which needed to be taken in order to create God's kingdom on Earth. From 64 to 313 AD, the faith was intermittently persecuted, but, following the Edict of Milan and the Conversion of Constantine, Christianity became the dominant faith in the empire, with Rome, Jerusalem, Alexandria, Antioch, and Constantinople becoming important centers of the faith.

Rise
Christianity started as a group of Jesus' male disciples and a handful of women, having around 20 adherents by 30 AD. Before his death, Jesus commanded his Twelve Apostles to go out and preach everywhere, spreading the "good news" of the New Testament to every person around the world. Originally, the Christian Church consisted entirely of Jews who believed in Jesus' resurrection, but Paul the Apostle began to spread the faith to the gentiles due to his belief that Jesus died for all humanity, not just the Jews. Small churches began to form in the eastern parts of the Roman Empire, and, by 64 AD, a sizeable church community had developed in the city of Rome itself.

Reasons for success
Christianity owed its rapid growth to its intolerant zeal, the doctrine of immortality, the miracles worked by the early Christians (which convinced pagans that God really was on the side of the Christians), strict morality, and a strong ecclesiastical organization, among many other causes. For most who came to Christianity, it meant abandoning the worship of other gods, making converting to the Christian faith different from anything else in the pagan world, as pagans were allowed to worship any god. In addition, many pagans were henotheists, believing in one god, but not ruling out the existence of other gods; seeing the miracles performed by Christians in God's name as proof that their god was the supreme one. Christians realized that many pagans were drawn to the idea of one ultimate divinity, and their belief in an ultimate god was not foreign to pagans.

Missionary work
Paul's idea of converting the world led to other missionaries converting the pagans, although, after Paul, the Church had no mission; most missionary work was spontaneous and voluntary. Gregory Thaumaturgus ("the Wonderworker") performed miracles in third-century Pontus, the fourth-century bishop Martin of Tours converted pagans in his own city of Tours in France, and the late-fourth-century bishop Porphyry closed pagan temples in Gaza and converted their devotees. Christians did not convert others through organized missionary efforts, but through using everyday social networks and word of mouth. Public gossip about the faith led to widespread interest in it, and adults who converted often converted their entire households (children and slaves included). This led to the exponential growth of the faith across the world.

The church did not spread through a well-thought-out and highly organized missionary endeavor, but instead through word of mouth and social networks, especially when it came to persuading the pagan reservoir to convert. It was not until the end of the 170s that non-Christians began to acknowledge the faith in their literature, and much of early Christian literature attributed supernatural miracles to the apostles.

Demographics
Between the time of Paul and the mid-2nd century, most converts to Christianity were lower-class and uneducated, especially during Paul's own day. Paul reminded the Corinthians about their own constituency, asking them to consider their calling; not many of them were wise by human standards, nor were they powerful or born to nobility, but God chose the foolish in the world to put to shame the wise, and chose the weak in the world to put to shame the strong. While the pagan philosopher Celsus decried Christianity for being a religion of "children" and gullible women (women were a clear majority in the churches of the third century), the church began to see intellectual converts during the mid-2nd century, including Justin Martyr in Rome, Tertullian in North Africa, and Origen in Alexandria.

Attractions of the Christian community
The Christian community was attractive for providing material support for its needy members, calling its members "brothers" and "sisters", and providing moral support for everyone who came. The Christian community provided enormous social benefits, and the nature of the community was a major cause in the faith's spread. One of the benefits was superior healthcare, ministering to the sick during times of illness. However, the early Christian churches were closed communities which did not allow for outsiders to join in worship services. The real cause for conversion was the disciples' abilities to perform miraculous deeds to convince outsiders that the Christian god was more powerful than any other, leading to them abandoning their older practices and joining the Christian ranks. The miracle of martyrdom helped to convince many pagans to join the faith, as the Christians' ability to endure torture, be obstinate in the fiath of suffering, and often die for their beliefs convinced others that they stood for the truth. Finally, the terrors of the afterlife scared many pagans - fearing eternal damnation in Hell - into converting to Christianity with the hope of enjoying eternal life in heaven.

Growth of the Church
Christianity was a minor faith for the first few centuries of its existence; it was not until 112 AD that Christians were mentioned by any pagan author. Pliny the Younger wrote to the emperor Trajan, discussing the Christian threat to the traditional cults and indicating that he had initiated an official proceeding against them. From 180 to 138, Christianity was not mentioned in any Roman source. The New Testament gave unrealistic accounts of the size of the Christian  Church; after Jesus' resurrection, the Christian cohort consisted of eleven disciples, several unnamed women, and the family members of Jesus, but the next verse in Acts of the Apostles mentioned 120 believers. In addition, a verse claimed that on Pentecost, 50 days after Jesus' crucifixion, 3,000 Jews were converted; soon thereafter, he converted 5,000 more, and, a chapter later, he converted multitudes more; at that rate, the Roman Empire would be Christian by 50 AD. Tertullian exaggerated the numbers of Christians even further by claiming that Christians constituted all but the majority in every city, and that they filled every place among the pagans. Christianity would remain minor up into the third century.

However, during the tenure of Pope Cornelius from 251 to 253 AD, the city of Rome had 46 presbyters, 7 deacons, 4 sub-deacons, 42 acolytes, 52 exorcists, readers, and doorkeepers, and 1,500 widows and other needy persons under church support; Adolf von Harnack surmised that the church had around 30,000-50,000 members at the time, just 5% of the population. Also during the third century, there were only a hundred bishops and churches in Italy. By the beginning of the foruth century, 7-10% of the empire was Christian, meaning that 4-6 million of the 60,000,000 Romans were Christian, with most of the Christians living in the eastern provinces.

Demographics of conversion
It proved much easier to convert people in urban settings than in rural ones, with dense populations making human interchange much more frequent than in rural settings; information about Christianity spread like wildfire. Christianity grew at different rates in different cities and regions, and there were far more converts in the East than the West in the first 300 years. It was not until the end of the 2nd century that the West began to be seriously Christianized. Even in Egypt, the people were almost entirely pagan for most of the time prior to the conversion of Constantine in 312 AD. However, the Christians had become half of the population between 318 and 330 AD, 75% by the mid-4th century, and 90% by the end of the century. By 312 AD, Christianity was nearly half the population in Asia Minor, Armenia, and Cyprus, less than half but very strong in Antioch, parts of Egypt, parts of Italy, and Spain, was sparse in Palestine, Phoenicia, and Arabia, and hardly existed at all in Italy, middle and upper Gaul, and Germany. Provincial capitals such as Rome, Antioch, and Thessalonica did not become predominantly Christan until the mid-4th century, and fairly large regional towns at the time were often roughly balanced between pagans and Christians. However, Athens, Delphi, and Gaza remained predominantly pagan even into the early 5th century.

Rate of Christian growth
The triumph of Christianity over paganism did not require a miracle, but instead steady growth for the first three centuries. Christianity grew at a rate of 30% per decade for the majority of the period; its growth was: If 25,000-30,000 Christians were added in the half-century between 100 and 150 AD, then at the very same rate of growth between 250 and 300 AD, something like 2,000,000 or 2,500,000 Christians would be added. Conversions included everyone who began to adopt Christian practices; if the head of a household converted and brought his wife and three children into the fold, there would be five new members. Family conversions occurred from the very beginning of the Christian movement, with Paul and his companions converting Lydia of Thyatira and her household at Philippi in Macedonia. He also baptized his jailer and his entire family without delay. By 100 AD, there were 50 named Christian communities. People converted because they knew other people who were Christian such as people connected to them in their daily lives, members of their families, friends, neighbors, and coworkers. After Christianity was legalized, the wealthy elite were able to construct Christian buildings with no dread of reprisal, and the masses could now join the faith wihtout fearing for their lives or property. Within eighty years of Constantine the Great's conversion, the transformation would be both massive and official; Rome would become predominantly and officially Christian.
 * 30 AD - 20 Christians
 * 60 AD - 1,000-1,500 Christians
 * 100 AD - 7,000-10,000 Christians
 * 150 AD - 30,000-40,000 Christians
 * 200 AD - 140,000-170,000 Christians
 * 250 AD - 600,000-700,000 Christians
 * 300 AD - 2,500,000-3,500,000 Christians
 * 312 AD - 3,500,000-4,000,000 Christians
 * 400 AD - 25,000,000-35,000,000 Christians